Honghuayuan Fm

It rests conformably on the shale at the top of the Tongzi Fm at the type section. In the reference section, it rests conformably on the thin- to medium-bedded limestone intercalated with yellowish green shale at the top of the Fenxiang Fm. In most regions, a conformable contact between the Honghuayuan Fm and the underlying strata is observed, and in eastern Yunnan, it rests disconformably on the Cambrian.

It is conformably overlain by the shale at the bottom of the Meitan Fm at the type section. In the reference section, is conformably overlain by the thick- to thin-bedded bioclastic limestone bearing glauconite at the bottom of the Dawan Fm. The upper boundary of this stratigraphic unit shows a diachronism. In Yichang, Hubei and Datianba in Xiushan, Sichuan, at the bottom of the overlying Dawan Fm find the Didymograptus deflexus, but in Huangjiazhai in Youyang, Sichuan and Chenjiahe in Yichang, Hubei, the Chitinozoa Eremochitina baculata zone corresponding to the lower part of the graptolite Didymograptus deflexus zone is found from the top of the Honghuayuan Fm, indicating a higher upper boundary for the Honghuayuan Fm in Huangjiazhai and Chenjiahe than in the type area. In most regions, a conformable contact between the Honghuayuan Fm and the overlying strata is observed.

With a persistent lithology, the Honghuayuan Fm varies considerably in thickness along the length of its outcrop. In Zhenghai, Eastern Yunnan, it recorded a thickness of 1-12 m; 10-170 m in south part of northern Guizhou and southeastern Guizhou; 22-80 m in southwestern and northeastern Sichuan; 13-80 m in western Hubei and northwestern Hunan; 12-71 m in eastern Hubei; 132-206 m in Ningzhen ranges; 24-141 m in southern Anhui. This stratigraphic unit can be correlated with the Dacao Fm in Northeastern Sichuan (Chen Junhan et al., 1988), Datan Fm at Susong and Hexian, Anhui (Zhang Quanzhong et al., 1966).